In the past there has been considerable study of the use of ultrasound in non-destructive testing and inspection of metals. Ultrasonic metal inspection is described in McGraw-Hill Encyclopedia of Science and Technology (1971) in volume 8 at page 340. Specific applications of ultrasound to metal inspection are described in U.S. Pat. Nos. 3,844,164 and 3,850,028.
Ultrasonic inspection apparatus heretofore available has not been well adapted for use in inspection of existing, in-use metal walls which have an extended vertical dimension such as oil refinery tanks, reaction vessels, distillation columns, steel ship hulls, and the like. Oil tanks, for example, are commonly inspected by attaching an ultrasonic transducer to a line. An operator positions himself on the top of the tank and using a winch pulls in the line, thus raising the ultrasonic transducer from ground level to the top of the tank, hopefully keeping reasonably good contact between the transducer and the tank wall surface as it rises. The ultrasonic transducer is then lowered to the ground, moved laterally and again raised to the top of the tank by the line and this procedure is repeated working around the circumference of the tank.
The present invention provides apparatus capable of making rapid and efficient inspection of vertical metal walls which are formed of a ferromagnetic material such as iron, steel and the like.